Patent GB-925234-A (GB)
Title: Improvements in or relating to apparatus for automatically reading line-trace characters
IPC: G06V10/40
Filed: 1960-02-10
Abstract: 925,234. Automatic pattern identification. WESTERN ELECTRIC CO. Inc. Feb. 10, 1960 [Feb. 26, 1959], No. 4681/60. Class 106 (1). A geometric pattern or a legible character is sensed in a recognition system to derive simultaneous signals representing the whiteness or blackness at points in a field of view which lie on a circle about a common centre and circuitry is provided to recognize the pattern or character from these signals. Sensing actually takes place in a series of concentric circles either dilating or contracting. This may be achieved by mechanically moving sensing elements synchronously from the centre of a pattern outwardly or by making a series of circular traces on a cathode-ray tube, projecting the beam on to the pattern, measuring the reflected light with a photo-cell and staticizing the signals derived. In the form shown in Fig. 2A, a circular array of photo-cells is provided, there being 64 radial lines of photo-cells with 32 in each. The pattern, a triangle as shown, is centred on the photo-cell array by a prescanning operation and rings of photo-cells are gated in succession to output lines one for each of the 64 radii. In the form of Fig. 4, this is done by a counter 45 operated by clock pulses from a source 46. The successive stages of the counter are connected to successive circle lines Cn+1, Cn and Cn+1. When the corresponding counter stage is operative the photocell 40-1, 40-2, &c. is connected by a diode 44-, 442 to the radial output lines r-1, r, &c. In other forms the read-out of each photo-cell in a radius is simultaneous but the signals are delayed so that they arrive at the output terminals in the proper succession by delay units, which may be all equal and serially connected between cells or graded and connected one between each cell and the output terminal The signals appearing at the outputs for each radius are applied to a threshold device 70-1, 70-2 &c. Fig. 7, to derive a " black " or " white " signal which passes to a register 71 having a two-state unit for each line. The storage unit is set by the first black signal to appear in the corresponding radius output and the time taken before setting is converted into a voltage amplitude by charging a condenser in the junction generator 72 from the beginning of the scan to the time of appearance of the first black signal. This voltage is therefore a measure of the distance from the centre point of the pattern in that particular radius. The 64 voltages, Fig. 2B, are applied to a comparator 73 which compares voltages on adjacent lines so as to detect the number of sudden changes. These correspond to the number of corners, e.g. three for a triangle, and they are counted by a counter 74 the output of which energizes the appropriate indicator 76. The system is invariant to size and, for symmetrical geometric patterns, to orientation also. Character recognition.-The character, which may be hand-written is centred with respect to the photo-cell array as shown in Figs. 10A, 11A, 12A and 13A and the photo-cell responses are shown in corresponding Figs. 10B, 11B, 12B and 13B. The character " 2 " generally produces an ascending line in the upper lefthand corner, Figs. 10B and 11B, corresponding to the curved portion in the upper right-hand section. The recognition is based upon rising O<SP>r</SP> falling lines such as this which can be expected in particular segments of the field, or definitely not expected. The presence of such lines is found by a comparison apparatus similar to that used above for the recognition of geometric patterns. In addition to rising or falling lines in particular zones the presence of double lines as in the upper part of the " 5 " Figs. 12A, 13A. This produces radii with two sets of black signals as shown in Figs. 12B, 13B. For the detection of this condition a second storage unit is provided for each radius which is set by a black signal occurring a predetermined period after the setting of the first unit. This period is imposed by a delay unit and prevents adjacent blacks belonging to the same line from setting the second storage unit. The second storage units corresponding to particular segments are gated together to test for the existence of a double line. For example, to allow for misshapen characters the double line detector circuit for character " 5 " may gate together outputs 1-5, dutputs 2-6, outputs 3-7, and outputs 4-8. The gates may consist of threshold devices which respond when, say, four of the five inputs are present. Their outputs are applied via an Or gate to an And gate to be combined with other " features present " or " features absent " signals to give an output on one of ten leads.